The role of the sympathetic nervous system and the renin-angiotensin system in maintenance of a high systemic vascular resistance in patients with congestive heart failure will be assessed by measurements of plasma catecholamines and plasma renin activity. The hemodynamic and neurohumoral response to a variety of physiologic stresses will be tested. Pharmacologic vasodilation will be produced both acutely and chronically to determine the relationship between clinical response, hemodynamic effects and the neurohumoral control of vascular resistance.